There is a continuing pressure to develop gas turbine engines having higher efficiencies, lower fuel burns, lower emissions and lower costs. As such, higher accuracy and consistency in the design of aerofoil blades are sought.
Flow in turbomachinery is inherently unsteady due to relative motion between a stationary blade row (stator) and a rotating blade row (rotor). The relevant components in the gas turbine engine include fans, compressors and turbines of various pressure ratios.
Computational fluid dynamics (CFD) has become an indispensable tool in blading design. However, a major source of uncertainty in CFD results follows from the treatment of turbulent flow. In the context of blade design applications, conventional CFD methods may use empirical turbulence models. While these models can be reasonably well-behaved for certain cases, e.g. in flow at a near design condition, there are also examples where the models struggle to produce adequately accurate and consistent results. In particular, compressor/fan off-design conditions, high pressure turbine heat transfer and cooling on blade surfaces in general, trailing edge and rotor tip regions, and transitional flow associated with loss generation for low pressure turbine blades.
Recent developments in computer hardware and numerical methods in CFD have led in the research arena to the emergence of turbulence eddy resolved methods. For example, large eddy simulations (LES) are a promising approach. These are described in Tucker, P. G. et al, Hybrid LES approach for practical turbomachinery flows—Part I: Hierarchy and example simulation, Journal of Turbomachinery, July 2012 in the context of stationary cascade configurations, and in Rodebaugh, G., Stratton, Z., Laskowski, G., and Benson, M, Assessment of Large Eddy Simulation Predictive Capability for Compound Angle Round Film Holes, ASME Paper GT2015-43602 in the context of simplified film cooling configurations with a single or few film cooling holes.
However, in the context of engine design, such LES approaches, which are confined to a single component in an isolated domain and are largely direct extensions of approaches developed for and applied to external flows (e.g. for aircraft wings), would lead to prohibitively high computing requirements. They are also in the main confined to a single blade passage and thus do not include intra blade row interaction effects. An exception is the study described in Rao, V. N., Tucker, P G, Jefferson-Loveday, R. J. and Coull, J. D., Large eddy simulations in low-pressure turbines: Effect of wakes at elevated free-stream turbulence, Int J of Heat and Fluid Flow, 2013. This includes some influences from an adjacent blade row for a low pressure turbine passage subject to incoming unsteady wakes simulated by upstream moving cylinders. However, this kind of LES analysis of flows with specified upstream disturbances still excludes mutual interactions between a blade row and its upstream neighbouring row.